Cre-recombinase under the control of mouse mammary tumor virus long terminal repeat (MMTV) was expressed in the salivary gland and mammary epithelial cells of adult mice, and induced recombination in all tissues.

Cre-recombinase under the control of the whey acidic acid protein was only detected in alveolar epithelial epithelial cells of mammary tissue during lactation, and transcription occurred at all stages of mammary development.